Films having a microfibrillated surface and method of making

Abstract

Fibers and microfibrillated articles are provided by imparting fluid energy to at least one surface of a highly oriented, voided, melt-processed polymeric film. The fibers and microfibrillated articles are useful as tape backings, filters, thermal and acoustical insulation and as reinforcement fibers for polymers or cast building materials such as concrete.

We claim:  
     
       1. An oriented film comprising a melt-processed immiscible mixture comprising a semicrystalline polymer component and a void initiating component, said film having at least one microfibrillated surface, said microfibrillated surface having a depth of greater than 10 micrometers. 
     
     
       2. The film of  claim 1  wherein said film has two microfibrillated surfaces. 
     
     
       3. A multilayer film wherein at least one layer comprises the film of  claim 1  and at least one additional layer. 
     
     
       4. The multilayer film of  claim 3  wherein said additional layer is selected from non-woven fabrics scrims or webs, woven fabrics or scrims, porous films, and non-porous films. 
     
     
       5. The film of  claim 1  wherein said void initiating component is an inorganic void initiating component selected from the group consisting of solid or hollow glass, ceramic or metal particles, microspheres or beads; zeolite particles; metal oxides; metal, alkali- or alkaline earth carbonates or sulfates; kaolin, talc, and carbon black. 
     
     
       6. The film of  claim 1  wherein said void initiating component is a polymer that forms an immiscible blend with said semicrystalline polymer component. 
     
     
       7. The film of  claim 1  wherein said first semicrystalline polymer is selected from the group of high and low density polyethylene, polypropylene, polyoxymethylene, poly(vinylidine fluoride), poly(methyl pentene), poly(ethylene-chlorotrifluoroethylene), poly(vinyl alcohol), poly(vinyl fluoride), poly(ethylene oxide), poly(ethylene terephthalate), poly(butylene terephthalate), nylon 6, nylon 66, polybutene, and thermotropic liquid crystal polymers. 
     
     
       8. The film of  claim 6  wherein said polymer blend is selected from the group of polypropylene and polybutylene terephthalate, polypropylene and polyethylene terephthalate, polypropylene and polystyrene, polypropylene and high density polyethylene, polypropylene and low density polyethylene, polypropylene and polycarbonate, polypropylene and polymethlypentene; and polypropylene and nylon. 
     
     
       9. The film of  claim 1  having a depth of microfibrillation of greater than 50 micrometers. 
     
     
       10. The film of  claim 1  having a depth of microfibrillation of greater than 500 micrometers. 
     
     
       11. The oriented film of  claim 1 , wherein said microfibrillated surface comprises polymeric microfibers of average effective diameter of less than 20 microns and having a transverse aspect ratio (width to thickness) of from 1.5:1 to 20:1. 
     
     
       12. The oriented film of  claim 1 , wherein said microfibrillated surface comprises polymeric fibrous flakes. 
     
     
       13. A filter comprising the microfibrillated film of  claim 1 . 
     
     
       14. An oil-absorbant article comprising the microfibrillated film of  claim 1 . 
     
     
       15. A wipe comprising the microfibrillated film of  claim 1 . 
     
     
       16. A process for preparing a film having a fibrous surface comprising: 
       a) providing a film comprising a melt-processed mixture comprising a semicrystalline polymer component and a void initiating component,  
       b) orienting said film to impart a voided morphology thereto, and  
       c) microfibrillating said film by imparting sufficient fluid energy to at least one surface of said film to a depth of greater than 10 micrometers.  
     
     
       17. The process of  claim 16  wherein said film is uniaxially oriented. 
     
     
       18. The process of  claim 16  wherein said film is biaxially oriented. 
     
     
       19. The process of  claim 16  wherein fluid energy is imparted with a high-pressure fluid. 
     
     
       20. The process of  claim 16  wherein said step of microfibrillating comprises subjecting said film to cavitation energy while immersed in a fluid. 
     
     
       21. The process of  claim 20  wherein said cavitation energy is ultrasonic cavitation energy. 
     
     
       22. The process of  claim 16  wherein said step of microfibrillating comprises contacting the film with one or more high-pressure fluid jets. 
     
     
       23. The process of  claim 22  wherein said fluid is water. 
     
     
       24. The process of  claim 16  wherein said polymer film is prepared by the steps of: 
       (a) extruding a melt-processible, immiscible mixture comprising a semicrystalline polymer component and a void initiating component;  
       (b) casting said polymer so as to maximize the crystallinity of said semicrystalline polymer component.  
     
     
       25. The process of  claim 16  wherein said polymer is stretched at a ratio of at least 5:1 to produce a highly oriented film having a plurality of voids. 
     
     
       26. The process of  claim 16  wherein the melt-processed semicrystalline polymer is selected from the group of high and low density polyethylene, linear low density polyethylene, syndiotactic polystyrene, polypropylene, polyoxymethylene, poly(vinylidine fluoride), poly(vinyl alcohol), poly(methyl pentene), poly(ethylene-chlorotrifluoroethylene), poly(vinyl fluoride), poly(ethylene oxide), poly(ethylene terephthalate), poly(butylene terephthalate), nylon 6, nylon 66, polybutene, and thermotropic liquid crystal polymers. 
     
     
       27. The process of  claim 16 , wherein said film is microfibrillated by imparting sufficient fluid energy to at least one surface of said film to a depth of greater than 50 micrometers. 
     
     
       28. The process of  claim 16 , wherein said film is microfibrillated by imparting sufficient fluid energy to at least one surface of said film to a depth of greater than 500 micrometers. 
     
     
       29. Thermal insulation media comprising the microfibrillated film of  claim 1 . 
     
     
       30. Acoustic insulation media comprising the microfibrillated film of  claim 1 .